Merge branch 'yinshunyu' into dev

尹顺宇学习笔记/尹顺宇11.08作业/尹顺宇11.08学习笔记.md

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+# Mybatis初步复习
+
+## 1.SpringBoot整合Mybatis
+
+## 1.1第一步添加依赖
+
+```
+<!--        mybatis启动器-->
+    
+        <dependency>
+            <groupId>org.mybatis.spring.boot</groupId>
+            <artifactId>mybatis-spring-boot-starter</artifactId>
+            <version>3.0.5</version>
+        </dependency>
+
+```
+
+
+
+###  1.2进行配置
+
+```
+#配置Mybatis
+mybatis:
+  configuration:
+    #在映射为java对象，将表中的下划线命名自动转换成驼峰式命名
+    map-underscore-to-camel-case: true
+    #日志前缀   可选
+    log-prefix: mybatis.
+    #日志实现类  可选
+    log-impl: org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl
+  #动态sql文件存储位置  
+  mapper-locations: classpath:/mapper/**/*.xml
+
+#配置日志显示sql
+logging:
+  level:
+    #指定日志前缀
+    mybatis: debug
+    
+
+```
+
+### 1.3 在Dao层编写的mapper接口，添加@Mapper注解
+
+![1762578862653](C:\Users\Administrator\AppData\Roaming\Typora\typora-user-images\1762578862653.png)
+
+### 1.4 编写动态sql文件（xx.xml文件）
+
+![1762578878514](C:\Users\Administrator\AppData\Roaming\Typora\typora-user-images\1762578878514.png)
+
+### 1.5 安装mybatisx插件
+
+![1762578934144](C:\Users\Administrator\AppData\Roaming\Typora\typora-user-images\1762578934144.png)
+
+安装之后在mapper和动态SQL文件对应代码左边有一个小鸟图标，方便直接跳转 
+
+![1762578917583](C:\Users\Administrator\AppData\Roaming\Typora\typora-user-images\1762578917583.png)
+
+## 2.自动映射
+
+当开启驼峰命名自动映射
+
+```yaml
+mybatis:
+  configuration:
+    map-underscore-to-camel-case: true
+```
+
+## 3.手动映射
+
+当自动映射无法满足需求时，可以使用 `<resultMap>` 进行精确的手动映射。
+
+```xml
+<resultMap id="唯一标识" type="要映射的Java类型">
+    <!-- 主键映射 -->
+    <id property="Java属性名" column="数据库列名"/>
+    
+    <!-- 普通字段映射 -->
+    <result property="Java属性名" column="数据库列名"/>
+    
+    <!-- 关联关系映射 -->
+    <association property="关联对象属性" javaType="关联对象类型"/>
+    <collection property="集合属性" ofType="集合元素类型"/>
+</resultMap>
+```
+
+举例：
+
+### 3.1基础字段映射
+
+```java
+实体类
+public class User {
+    private Long userId;           // 与数据库字段名不同
+    private String userName;       // 需要手动映射
+    private String email;
+    private Integer status;
+    private LocalDateTime createTime;
+    private LocalDateTime updateTime;
+    
+    // 构造函数、getter、setter...
+}
+```
+
+```sql
+数据库表结构：
+CREATE TABLE t_user (
+    id BIGINT PRIMARY KEY,
+    name VARCHAR(50),
+    email VARCHAR(100),
+    status TINYINT,
+    created_at DATETIME,
+    updated_at DATETIME
+);
+
+```
+
+```xml
+<!-- 基础手动映射示例 -->
+<resultMap id="BaseUserMap" type="User">
+    <!-- 主键字段，使用 id 标签 -->
+    <id property="userId" column="id"/>
+    
+    <!-- 普通字段，使用 result 标签 -->
+    <result property="userName" column="name"/>
+    <result property="email" column="email"/>
+    <result property="status" column="status"/>
+    <result property="createTime" column="created_at"/>
+    <result property="updateTime" column="updated_at"/>
+</resultMap>
+
+<!-- 使用 resultMap -->
+<select id="selectUserById" resultMap="BaseUserMap">
+    SELECT id, name, email, status, created_at, updated_at
+    FROM t_user
+    WHERE id = #{id}
+</select>
+```
+
+说明：
+
+![1762581420222](C:\Users\Administrator\AppData\Roaming\Typora\typora-user-images\1762581420222.png)
+
+### 3.2一对一关联映射
+
+#### 3.2.1单次查询嵌套结果映射
+
+举例：
+
+```java
+实体类
+public class User {
+    private Long userId;
+    private String userName;
+    private UserProfile userProfile; // 一对一关联
+    // getter/setter...
+}
+
+public class UserProfile {
+    private Long profileId;
+    private Long userId;
+    private String realName;
+    private Integer age;
+    private String address;
+    private String phone;
+    // getter/setter...
+}
+```
+
+```xml
+手动映射配置：
+<!-- 用户和用户详情的一对一映射 -->
+<resultMap id="UserWithProfileMap" type="User">
+    <id property="userId" column="id"/>
+    <result property="userName" column="name"/>
+    
+    <!-- association: 一对一关联映射 -->
+    <association property="userProfile" javaType="UserProfile">
+        <id property="profileId" column="profile_id"/>
+        <result property="userId" column="id"/> <!-- 注意：这里复用外层查询的id -->
+        <result property="realName" column="real_name"/>
+        <result property="age" column="age"/>
+        <result property="address" column="address"/>
+        <result property="phone" column="phone"/>
+    </association>
+</resultMap>
+
+<!-- 关联查询SQL -->
+<select id="selectUserWithProfile" resultMap="UserWithProfileMap">
+    SELECT 
+        u.id, u.name,
+        up.id as profile_id, up.real_name, up.age, up.address, up.phone
+    FROM t_user u
+    LEFT JOIN t_user_profile up ON u.id = up.user_id
+    WHERE u.id = #{userId}
+</select>
+```
+
+#### 3.2.2 多次查询嵌套查询映射 
+
+```xml
+<!-- 主结果映射 -->
+<resultMap id="UserWithProfileNestedMap" type="User">
+    <id property="userId" column="id"/>
+    <result property="userName" column="name"/>
+    
+    <!-- 嵌套查询：通过 select 属性引用另一个查询 -->
+    <association property="userProfile" column="id" 
+                 select="selectUserProfileByUserId"/>
+</resultMap>
+
+<!-- 主查询 -->
+<select id="selectUserWithProfileNested" resultMap="UserWithProfileNestedMap">
+    SELECT id, name
+    FROM t_user
+    WHERE id = #{userId}
+</select>
+
+<!-- 嵌套查询 -->
+<select id="selectUserProfileByUserId" resultType="UserProfile">
+    SELECT 
+        id as profileId, 
+        user_id as userId,
+        real_name as realName,
+        age, address, phone
+    FROM t_user_profile`
+    WHERE user_id = #{userId}
+</select>
+```
+
+
+
+### 3.3一对多集合映射
+
+```java
+实体类：
+public class User {
+    private Long userId;
+    private String userName;
+    private List<Order> orders; // 一对多关联
+    // getter/setter...
+}
+
+public class Order {
+    private Long orderId;
+    private Long userId;
+    private String orderNumber;
+    private BigDecimal amount;
+    private LocalDateTime orderTime;
+    // getter/setter...
+}
+```
+
+```xml
+<!-- 用户和订单的一对多映射 -->
+<resultMap id="UserWithOrdersMap" type="User">
+    <id property="userId" column="id"/>
+    <result property="userName" column="name"/>
+    
+    <!-- collection: 一对多关联映射 -->
+    <collection property="orders" ofType="Order">
+        <id property="orderId" column="order_id"/>
+        <result property="userId" column="id"/> <!-- 注意：这里复用外层查询的id -->
+        <result property="orderNumber" column="order_number"/>
+        <result property="amount" column="amount"/>
+        <result property="orderTime" column="order_time"/>
+    </collection>
+</resultMap>
+
+<!-- 关联查询SQL -->
+<select id="selectUserWithOrders" resultMap="UserWithOrdersMap">
+    SELECT 
+        u.id, u.name,
+        o.id as order_id, o.order_number, o.amount, o.order_time
+    FROM t_user u
+    LEFT JOIN t_order o ON u.id = o.user_id
+    WHERE u.id = #{userId}
+</select>
+```
+
+### 3.4复杂的多层嵌套
+
+```java
+public class User {
+    private Long userId;
+    private String userName;
+    private List<Order> orders;
+}
+
+public class Order {
+    private Long orderId;
+    private String orderNumber;
+    private List<OrderItem> orderItems;
+}
+
+public class OrderItem {
+    private Long itemId;
+    private Long productId;
+    private Integer quantity;
+    private Product product; // 关联商品
+}
+
+public class Product {
+    private Long productId;
+    private String productName;
+    private BigDecimal price;
+}
+```
+
+```xml
+<!-- 完整的多层嵌套映射 -->
+<resultMap id="CompleteUserMap" type="User">
+    <id property="userId" column="user_id"/>
+    <result property="userName" column="user_name"/>
+    
+    <!-- 第一层嵌套：订单集合 -->
+    <collection property="orders" ofType="Order" resultMap="OrderWithItemsMap"/>
+</resultMap>
+
+<resultMap id="OrderWithItemsMap" type="Order">
+    <id property="orderId" column="order_id"/>
+    <result property="orderNumber" column="order_number"/>
+    
+    <!-- 第二层嵌套：订单项集合 -->
+    <collection property="orderItems" ofType="OrderItem" resultMap="OrderItemMap"/>
+</resultMap>
+
+<resultMap id="OrderItemMap" type="OrderItem">
+    <id property="itemId" column="item_id"/>
+    <result property="quantity" column="quantity"/>
+    
+    <!-- 第三层嵌套：商品信息 -->
+    <association property="product" javaType="Product">
+        <id property="productId" column="product_id"/>
+        <result property="productName" column="product_name"/>
+        <result property="price" column="price"/>
+    </association>
+</resultMap>
+
+<!-- 复杂查询SQL -->
+<select id="selectUserWithOrderDetails" resultMap="CompleteUserMap">
+    SELECT 
+        u.id as user_id, u.name as user_name,
+        o.id as order_id, o.order_number,
+        oi.id as item_id, oi.quantity,
+        p.id as product_id, p.name as product_name, p.price
+    FROM t_user u
+    LEFT JOIN t_order o ON u.id = o.user_id
+    LEFT JOIN t_order_item oi ON o.id = oi.order_id
+    LEFT JOIN t_product p ON oi.product_id = p.id
+    WHERE u.id = #{userId}
+    ORDER BY o.order_time DESC, oi.id
+</select>
+```
+
+### 3.5.注意
+
+1.可以 自动映射与手动映射结合
+
+```xml
+<!-- 混合映射：autoMapping="true" 开启自动映射 -->
+<resultMap id="HybridUserMap" type="User" autoMapping="true">
+    <!-- 只手动映射名称不匹配的字段 -->
+    <id property="userId" column="id"/>
+    <result property="userName" column="name"/>
+    <result property="createTime" column="created_at"/>
+    
+    <!-- 关联对象也可以使用自动映射 -->
+    <association property="userProfile" javaType="UserProfile" autoMapping="true">
+        <id property="profileId" column="profile_id"/>
+        <!-- 只覆盖需要特殊处理的字段 -->
+        <result property="realName" column="real_name"/>
+    </association>
+</resultMap>
+```
+
+##
+